The mismanagement and neglect of Arlington National Cemetery that led to hundreds of veterans’ graves being either mislabeled or lost now appears much more far-reaching than officials previously disclosed, according to a Senate hearing Thursday.

The number of misidentified graves could be as high as 6,600, said Sen. Claire McCaskill, chairwoman of an oversight panel on the Senate Homeland Security and Government Affairs. The Army inspector general’s office had recently estimated the number at only 221.

Right now, just three of the cemetery’s 70 sections that hold a total of roughly 330,000 graves have been examined.

Ms. McCaskill, Missouri Democrat, and Massachusetts Sen. Scott Brown, the panel’s ranking Republican member, cited poor recordkeeping, contract problems and oversight by Army officials. But they directed most of their outrage and frustration toward former cemetery Superintendent John C. Metzler Jr., who acknowledged knowing about the identification problems as far back as 2003.

“The notion that you would come in here and didn’t know about [problems] until a month ago is offensive,” Ms. McCaskill said. “You did know about it and you did nothing.”

Mr. Metzler, a former Army helicopter pilot who managed the cemetery from 1990 until retiring in 2010 amid press reports about the problems, took responsibility for the mistakes.

“Personally, it is very painful for me that our team at Arlington did not perform all aspects of its mission to the high standard required,” he said. “I was the senior government official in charge and I accept full responsibility for all of my actions and my team’s actions.”

“I’d have a lot of fun with you in a deposition because I don’t think we’re getting straight talk here,” said Mr. Brown, an attorney.

Most of the questions by the senators focused on why the cemetery still uses a paper system to check graves and has no computer-based system, despite spending as much as $8 million in contracts to make the transition.

Thurman Higginbotham, the cemetery’s deputy secretary who also retired last year, declined to answer most questions, invoking his Fifth Amendment rights against self-incrimination.